Fluid device



0. L. WOOD FLUID DEVICE March 17, 1970 3 Sheets-Sheet 1 Filed Dec. 30,1966 0. L. WOOD FLUID DEVICE March 17, 1970 3 Sheets-Sheet 2 Filed Dec.50, 1966 8 I2 1a 2a 24 JEcoA/LWEY sup er P865502! I b Pemqey su /wP65950185 mmar PEA-$51125 fps/ 0- L. WOOD FLUID DEVICE March 17, 1970 3Sheets-Sheet 3 Filed Dec. 30, 1966 N u 2 ma 1 j .n 5 k A T :c 14 4 I 1 11 13 w a W \N l2 2 i |i l1. 1 a a W M ,M i

United States Patent US. Cl. 13781.5 24 Claims ABSTRACT OF THEDISCLOSURE A fluid amplifier having high gain and high pressure recoverycharacteristics including a supply nozzle for providing a first fluidstream into a low pressure region, a receiver positioned opposite thesupply nozzle having a conical configuration with an orifice at the apexof the cone with a first passage in the receiver communicating with theorifice for supplying a second supply stream which impacts with the mainsupply stream adjacent the tip of the receiver, a discrete outlet fluidpassage in the receiver also communicating directly with the orifice thelatter being angularly aligned in one state with the resulting flowvector between the first and second supply streams, such that as themomentum flux of the first supply stream is varied the fiow streamresulting from the interaction of the first and second streams will moveaway from the discrete outlet passage toward the low pressure region.

This invention relates generally to fluid devices and more particularlyto a pure fluid device having high pressure recovery characteristics.

The recently developing technology of pure fluid devices involves thecontrol of fluid power systems by devices in which the fluid itself isthe working medium. Many fluid devices known today adopt the phenomenaof Wall attachment or stream interaction to perform control, sensing andlogic functions. Fluid amplifiers, referred to in the art as activeelements, have the capability of responding to small changes in a lowenergy fluid control signal to cause relatively great changes in ahigher energy output signal, much like an electronic amplifier.

The presently known pure fluid devices include the jet deflectionamplifier, vortex devices, the double leg elbow amplifier and thetransverse impact modulator amplifier, these being merely exemplary.Although these devices are generally considered proportional elements,they may also be designed to permit digital or on-oil response, ifdesired.

The operating performance of fluidic amplifiers may be evaluated interms of pressure and flow recovery, pressure and flow gain, and signalto noise ratio, among other criteria. The pressure recovery of thedevice is defined as the proportion of output flow pressure to thesupply flow pressure under maximum recovery conditions. Flow recovery isdefined in the same way with respect to flow. Pressure or flow gainrefers to the ratio of change of the output flow to the change of thecontrol flow input with the power stream remaining unchanged. Lastly,the signal to noise ratio is the ratio of the maximum output signal tothe maximum noise level experienced. It is, of course, desirable todesign circuit devices which have a high signal output with very littlenoise and thus a high signal to noise ratio.

Prior known fluid amplifiers have had relatively low pressure recoveryand loW signal to noise characteristics. One such prior device, theimpact modulator amplifier, and more particularly the transverse impactmodulator, employs the concept of deflecting one of two alignedimpacting power jets, the latter being maintained at constant supplypressures. The impacting jets produce a radial flow cone, the balancepoint of which is controlled by 3,500,846 Patented Mar. 17, 1970 varyingthe momentum flux of one of the supply jets or by a transverse controljet. To capture this flow cone and produce an output, an annularcollection chamber is provided normally aligned with the flow cone. Byreducing the momentum flux with the application of a control signal, thebalance point of the flow cone moves away from the annular collectionchamber thereby providing an amplifier with negative gaincharacteristics. As the efiiciency of the collection chamber is low, thepressure recovery of the transverse impact modulator is also relativelylow and the noise level is quite high at low frequencies. In efiect, thecollection chamber serves as a noise generator.

In accordance with the present invention, a proportional fluid amplifieris provided which not only has high pressure recovery characteristics,but also a high signal to noise ratio. The device incorporates primaryand secondary power jets flowing in generally opposite directions withthe jets being angularly related. An outlet or receiving duct ispositioned so that the momentum vector of the flow resulting from theinteraction of the two power jets is aligned therewith. This alignmentleads to a much higher pressure recovery than heretofore known indevices of this character. With the application of a control flowagainst one of the power jets, the momentum flux thereof is reduced sothat the interaction region between the two power jets moves axially,and the angle of the momentum vector increases, thus reducing the flowin the output duct. The output flow varies in an inverse proportionalmanner with the control flow, and hence in the embodiment disclosedherein the amplifier is a negative gain proportional amplifier.

It is, therefore, a primary object of the present invention to provide anew and improved fluidic device.

Another object of the present invention is to provide a new and improvedproportional amplifier having a higher pressure recovery characteristicthan heretofore known in the prior art, with a low noise factor.

A more specific object of the present invention is to provide a fluidicdevice having two generally opposed angularly related power jets withthe momentum vector of the flow resulting from the interaction of thetwo jets being aligned in at least one state with a discrete outletpasssage or duct.

Another object of the present invention is to provide a new and improvedfluid amplifier of the type described above having a receiver in thepath of flow of one of the power jets with passages therein intersectingapproximately at the tip of the receiver, one of the passages definingthe other power jet and the other passage defining the output ductarranged so that the power jets interact at or within the tip of thereceiver in one state and upon variation in the moment flux in one ofthe power jets the interaction of the two power jets will move out of oraway from the receiver tip causing the momentum vector of the resultingflow of the two power jets to at least partially miss the output duct.

A still further object of the present invention is to provide a new andimproved fluid amplifier of the type described immediately above inwhich the intersection of the two passages at the tip of the receiverdefines a receiver orifice of generally elliptical shape with thedimension of the orifice being optimized to provide maximum pressurerecovery and low noise.

Another object of the present invention is to provide a new and improvedfluid amplifier of the type described above in which the axial distancebetween the primary one of the power jets and the receiver tip isoptimized to provide maximum pressure recovery in the outlet duct.

It is a still further object of the present invention to provide a newand improved fluid amplifier of the type described above with a controljet for varying the momentum flux of one of the power jets with thedimensional location of the control jet with respect to the power jet ornozzle being optimized to provide a high pressure gain.

Another object of the present invention is to provide a new and improvedfluid amplifier of the type described generally above having a supplyjet nozzle which con tributes greately to a high pressure recoverydevice.

Other objects and advantages will be apparent from the followingdetailed description taken in connection with the accompanying drawingsin which:

FIG. 1 is a top elevation, partially in cross-section, showing a fluidamplifier according to the present invention;

FIG. 2 is a subassembly view taken generally along line 22 of FIG. 1showing the receiver tip;

FIGS. 3 and 4 are diagrammatic views illustrating the operation of thepresent device;

FIG. 5 is a curve showing the variation in output pressure as a functionof the primary supply pressure;

FIG. 6 is a curve showing the variation in output pressure as a functionof the secondary supply pressure;

FIG. 7 is a curve showing the pressure recovery as a function of theratio of the major to minor orifice diameters for various receivers;

FIG. 8 is a curve showing the overall pressure gain as a function of themajor to minor receiver orifice diameters for various receivers;

FIG. 9 is a curve showing the percent flow recovery as a function of theratio of the major to minor orifice diameters for the various receivers;

FIG. 10 is a curce showing the overall flow gain as a function of theratio of the major to minor orifice diameters for the various receivers;and

FIG. 11 is a curve showing the output pressure as a function of thecontrol pressure for various control nozzle angles.

While I have shown and shall hereinafter describe one embodiment of theinvention, it is to be understood that it is capable of manymodifications. Changes, therefore, in the construction and arrangementmay be made without departing from the spirit and scope of the inventionas defined in the appended claims.

Referring to the drawings and particularly FIGS. 1 and 2, a fluidamplifier 10 according to the present invention is seen to consistgenerally of a primary supply nozzle 11, a control nozzle 13 and areceiver 15 having defined therein a secondary supply nozzle 16 and anoutlet duct or passage 17.

More specifically, a generally U-shaped frame or fixture 20 is provideddefining with the receiver 15 a low pressure central region 22. Theprimary supply nozzle 11 is mounted within the frame or fixture 20 andextends into the low pressure region 22. Nozzle 11 includes an upstreamconical portion 24 and a reduced downstream exit portion 26. A suitablefitting 28 fixed to one side of the fixture 20 is adapted to beconnected to a suitable source of supply (not shown) under pressure PFluid device 10 will operate under either a gaseous or liquid fluid,although development of the device thus far has proceeded mainly withthe use of gaseous fluid, such as air. As will appear hereinafter theaxis 30 of the primary supply nozzle is employed as a reference for thelocation of the various other portions of the device.

The receiver 15 has a generally rectangular portion 32 mounted betweenthe legs of the U-shaped frame member 20 by suitable threaded fasteners33. Extending towards the primary supply nozzle 11 from the rectangularportion 32 is a generally conical portion 35 having a flat tip 36. Aknife edge is provided at 38 for improving the operation of the device.

As shown in the drawings, the axes of the passages 16 and 17 define anincluded angle of approximately thirty degrees with the axis 30 ofnozzle 11 bisecting this angle. However, this is only a preferredrelationship and the axis of passage 16 may define a lesser or greaterangle with respect to the axis 30 as long as the angle is somewhatgreater than zero. Furthermore, the axis of passage 17 may, if desired,define with the axis 30 an angle greater or less than the fifteendegrees shown.

Suitable fittings 36 and 37 fixed to the receiver 32 communicaterespectively with the passages 16 and 17. Fitting 36 is adapted to beconnected to the source for supplying fluid under pressure P to thesecondary supply duct 16. As will appear more clearly hereinbelow, it isusually desirable to provide a pressure drop between P and P although insome instances under certain conditions they may be equal. A suitabledropping resistor may be provided between the fittings 28 and 36 for theformer purpose. However, due to the non-linearities in a droppingresistor, the amplifier would not be optimumly operable over a widepressure range. One solution to this problem is to select the diameterof the secondary supply passage 16 smaller than the diameter of thenozzle passage 26 so that the momentum flux from the secondary supplyjet 16 is less than that from nozzle 11 even though the fluid pressurein both is equal.

The outlet fitting 37 is adapted to connect the outlet passage to theload .(not shown) The axes of passages 16 and 17 intersect somewhatoutside the receiver towards the nozzle 11 so that the passages open atthe tip surface 36 defining therein a generally elliptical orifice 40.Further, the passages 16 and 17 define splitter 41, and an area 43within the receiver which is the interaction region for the primary andsecondary jet flow. The axis 30 of the primary jet nozzle 11 preferablybisects the splitter 41. As will appear hereinafter the depth of thesplitter 41, the size of the orifice 40 and the sizes of the variouspassages and outlets have a profound affect upon the performancecharacteristics of the present device.

For varying the momentum flux of the primary supply jet from nozzle 11,the control nozzle 13 is provided which communicates with a suitablefitting 45. Fitting 45 is adapted to be connected to a regulatablesource of control fluid, at a pressure which is a small percentage ofthe primary and secondary supply pressure. Control flow from the nozzle13 deflects the primary supply jet from nozzle 11 thus reducing themomentum flux of the primary stream and varying the output flow in duct17.

The operation of the device as thus far described will be apparent froma reference to FIGS. 3 and 4. With fluid pressure P applied to nozzle11, e.g. 35 p.s.i.g. and fluid pressure P applied to secondary supplyjet passage 16, e.g. 32 p.s.i.g., the primary and secondary jetstherefrom impinge on one another. The ratio of the primary supply jetpressure to the secondary supply jet pressure (P /P is adjusted to givea maximum pressure recovery in the output passage 17. The outputpressure can have an infinite number of values by setting the primarypower pressure P and then adjusting the secondary power pressure P toobtain the proper ratio. If the primary power nozzle 11 is subsonic, amaximum output pressure can be obtained in duct 17 of approximately 50p.s.i.a. Much higher output pressures can be obtained, however, if theprimary power nozzle 11 is supersonic. With the proper selection of theratio P /P the primary and secondary power jets will interact adjacentthe region 43 and the momentum vector of the flow resulting from theinteraction of the two power jets will be aligned with the output duct15. This alignment contributes to a high pressure recoverycharacteristic.

With control flow present in control nozzle 13, as shown in FIG. 4, thecontrol fluid stream strikes the primary jet stream from nozzle 11 inthe low pressure region 22. This reduces the momentum flux of theprimary power jet or stream and deflects it so that it no longerinteracts with the secondary power jet in region 43. Instead, the twopower jets interact in low pressure region 22 and the momentum vector ofthe flow resulting from the interaction of the two power jets increasesits angular relationship with duct 17 and is no longer directed to andaligned with respect to the output duct. In this situation no outputflow is captured by the output duct 17 and in fact flow may actually beentrained through the output duct. Of course, as this is a proportionalamplifier, the momentum flux of the primary power jet may be reduced ordeflected a lesser amount resulting only in a reduced flow through theoutput duct 17. The output flow varies in an inverse proportional mannerwith the control flow, and the control flow through nozzle 13, requiredto modulate the output flow, is low compared to the output flow. Hence,the present amplifier is a negative gain proportional fluid amplifier.

The control nozzle 13 is coplanar with the primary supply nozzle 11 andpassages 16 and 17 to provide the optimum pressure and flow gain. Oncethe control flow from nozzle 13 has deflected the primary supply flowfrom nozzle 11, the secondary supply flow from passage 16 aids infurther deflection of the primary supply flow away from the receiver tip36. This characteristic enhances the pressure and flow gain of thepresent device.

The pressure gains in several devices constructed in accordance with thepresent invention have been found to be about thirty to one with gainsas high as sixty to one in selected portions of curves illustrating theoutput pressure as a function of control pressure with the devicedriving an infinite impedance.

The control jet 13 is only a preferable means for varying the momentumflux of the primary jet from nozzle 11 and other means may be providedin place of this to deflect, constrict, or in some other manner disturbthe primary jet. Such means may include electrophoresis devices, anelectromagnetic device with ionized supply flow,

evices which restrict the primary power flow with an annular concentriccontrol flow, etc.

Shown in FIG. 5 is a curve showing the variation in dead-ended outputpressure for the present amplifier, plotted as a function of the primarysupply pressure P with the secondary supply pressure P constant, andadjusted to give maximum pressure recovery when the primary supplypressure is 20 p.s.i.g. Note that the pressure recovery, i.e., theproportion of output pressure to primary supply pressure, is in excessof ninety percent. The curve in FIG. 6 illustrates the variations inoutput pressure (dead-ended) as a function of the secondary supplypressure P with the primary supply pressure at 20 p.s.i.g. Note that thevariation in the output pressure is quite gradual.

The flow gains in the present device are on the order of approximatelyten to One. Flow recovery can be increased, if desired, at the expenseof pressure recovery by increasing the diameter of the duct 17 withrespect to the other ducts. While the present device as above describedhas many basic performance characteristics superior to those inheretofore known proportional fluid amplifiers, the geometricconfiguration and location of the various ducts, jets and passagesdescribed have a further influence over these performancecharacteristics. The following dimensional analysis is an optimizationof the fluid amplifier configuration for low noise level and highpressure recovery characteristics.

The configuration of the primary nozzle. 11 has a significant affect inobtaining high pressure recovery. In order to have fully establishedpipe flow in the nozzle, the axial length of the reduced circularpassage 26 should be at least ten times the diameter of that passage.Furthermore, the angle 50 of the conical portion 24 should beapproximately thirty degrees for maximum pressure recovery.

As described above, the receiver orifice 40 is generally elliptical asit is formed by two circular ducts intersecting each other adjacent thetip of the receiver. The ratio of the major diameter Z to the minordiameter W (FIG. 2) and the depth 53 from the tip of the receiver to thesplitter 41 are determined by the point of intersection of the two ductcenter lines with respect to tip 36 for any given ducts. The aifect ofthe shape, of the orifice 40 on pressure gain and noise is significant.Increasing the major axis Z reduces the noise generated in theamplifier. Apparently, the chief source of noise is the interaction ofthe secondary and primary supply jets in the receiver. When the receiverorifice 40 is enlarged, i.e. by reducing the splitter depth 53 from tip36, the influence of the receiver tip on the secondary supply jet isdiminished because the distance from the tip to the free jet isincreased. The equation for the size of the orifice 40 with respect tothe depth of the splitter 41 and the included angle between the passages16 and 17 is where d splitter depth, Z=major orifice diameter, W=minororifice diameter, t9=the included angle between the ducts 16, 17.

With the size of the ducting and passages as follows: nozzle 13, 0.040inch; nozzle 11, 0.040 inch; passage 16, 0.031 inch; and passage 17,0.031 inch; with the angle (0) between the ducts being thirty degreesand bisected by the axis 30, a receiver having a ratio Z/ W (major tominor axis ratio) of 1.39 has been found optimum from the standpoint ofminimum noise.

The pressure recovery, pressure gain, flow recovery and the flow gainfor four actual receivers 15 i.e. a, b, c and d, constructed inaccordance with the present invention are given as a function of Z/W inFIGS. 7, 8, 9 and 10. During all the tests from which this data wasobtained the primary supply pressure was at 20 p.s.i.g. The various Z/ Wratios were obtained on the receivers by removing material from thereceiver tip 40, thus increasing the Z/ W ratio.

Referring to FIG. 7, it may be seen that the percent pressure recoveryremains fairly constant for increasing values of Z/ W up to about 1.28and then begins to decrease. As indicated in FIG. 8, the overallpressure gain of these receivers generally increases with an increase ofZ/ W, reaches a maximum and then begins to decrease. For three of thereceivers the overall gain reaches a maximum approximately at 1.28 Z/ W,and as shown in FIG. 9 the flow recovery for three of the four receiversremains fairly constant over a wide range of Z/ W.

The overall flow gain, illustrated in FIG. 10, does not vary appreciablyfor receivers a, b, and c for values of Z/W greater than 1.15.

It has been found apparent from the above data, presented only insummary form, and from other data, that the optimum ratio of Z/ W forlow noise the device is approximately 1.39. Further, Z/ W ratio for highpressure recovery combined with high overall pressure gain isapproximately 1.28. Further, as the percent flow recovery and theoverall flow gain do not vary significantly about either of these valuesof Z/ W they do not alter the optimum ratios determined for noise andpressure recovery and gain.

The axial distance L between the end of the nozzle 11 and the receivertip 36 has an effect on pressure recovery and pressure gain. For lowervalues of primary supply pressure in the range of 2 to 20 p.s.i.g., thepressure recovery varies slowly with changes in L between 0.12 and 0.195inch. However, for a primary supply pressure of 35 p.s.i.g., thevariation in pressure recovery with changes in L is more pronounced andthe optimum value for L is substantially 0.180 inch.

The configuration of the primary supply nozzle 11 has an affect on theoptimum value L due to the fact that at high supply pressures diamondshaped shock patterns develop downstream from the primary supply nozzle.Furthermore, the overall pressure gain increases for both low and highprimary supply pressures as the distance L increases. However, since thepressure recovery decreases above L=0.180, and since the noise increasesas Well above this value, it appears to be the optimum.

As shown in FIG. 11, the pressure gain varies as a function of the angle60 (FIG. 1) between the control nozzle 13 and the axis 30 of the primarysupply jet 11. As may be seen in FIG. 11 the lowest gain is with anangle of ninety degrees and the highest gain is with an angle of 75degrees with the control flow slightly opposing the primary flow.However, the gain is almost as good at 82 degrees and the linearity isthe best at this angle.

I claim:

1. A fluid amplifier, comprising: first means for establishing a supplystream, second means for establishing a second supply stream impingingon said first stream in a direction generally opposite said firststream, receiving means having an opening for receiving fluid from theinteraction of said streams, said second means directing said secondstream at an angle to said first stream to deflect the same toward saidreceiving means, means for disturbing one of said streams so that theinteraction region of said streams moves relative to said receivingmeans, said second means for establishing said second supply streambeing in said receiving means and communicating with said opening on theside thereof opposite said first means, and at least one discrete outletpassage in said receiver communicating directly with said opening on theside of said opening opposite said first means, said discrete outletpassage being not significantly greater in size than said first meansfor establishing a supply stream.

2. A fluid amplifier as defined in claim 1, wherein said first means,said second means and said receiving means lie in a common plane.

3. A fluid amplifier as defined in claim 1, including frame means havinga low pressure central region, said first means including a primarysupply nozzle mounted in said frame means and extending into said lowpressure region, a receiver member in said frame means and having areceiver tip disposed generally in the path of flow from said primarysupply nozzle, said receiver member having a first passage opening tosaid tip and defining said second means, said receiver member havingsaid outlet passage intersecting said first passage substantially atsaid receiver tip and defining an orifice in said receiver member.

4. A fluid amplifier as defined in claim 3, wherein said modifying meansincludes a control nozzle mounted in said frame means and extending intosaid low pressure region for directing control fluid adjacent said firststream.

5. A fluid amplifier, comprising: first means for establishing a firstsupply stream, second means for establishing a second stream impingingon said first stream in a direction generally opposite said firststream, receiver means having an orifice for receiving fluid from theinteraction of said streams, said second means being in said receivermeans and directing said second stream at an angle to said first streamto deflect the same and being on the side of said orifice opposite saidfirst means, discrete outlet passage means in said receiver meanscommunicating directly with said orifice on the side thereof oppositesaid first means, and means for modifying one of said streams so thatthe angle of the flow vector of the fluid stream resulting from theinteraction of said first and second streams changes with respect tosaid outlet passage means, said first and second supply streamestablishing means being constructed so that the flow vector from theinteraction of said streams is aligned with said outlet passage means inthe absence of said modifying means.

6. A fluid amplifier as defined in claim 5, wherein said means formodifying one of said streams includes means for disturbing the firststream upstream of the interaction of said first and second streams toreduce the momentum flux of said first stream.

7. A fluid amplifier as defined in claim 6, including a receiver portionspaced axially from said first means, first passage means in saidreceiver having an axis intersecting the axis of said first means anddefining said second means, said outlet passage means in said receiverportion having an axis intersecting the axis of said first passage, thereceiver portion defining an interaction region for the first and secondstreams.

8. A fluid amplifier as defined in claim 7, wherein said first means andsaid first and outlet passage means are located so that with fluidflowing in said first means and in said first passage means under apredetermined relative pressure, the vector of the flow resulting fromthe interaction of said first and second streams is angularly alignedwith said outlet passage means.

9. A fluid amplifier is defined in claim 8, wherein said means formodifying one of said streams includes means for reducing the momentumflux of said first stream whereby said resulting flow will move awayfrom said second passage means so that the amplifier has a negative gaincharacteristic.

10. A fluid amplifier as defined in claim 9, wherein said means forreducing the momentum flux of said first stream includes a controlnozzle for directing control fluid against said first stream.

11. A fluid amplifier as defined in claim 10, wherein the axis of saidcontrol nozzle defines an angle of between 70 and degrees with the axisof said first means in a direction so that the control flow opposes thefirst stream.

12. A fluid amplifier as defined in claim 11, wherein said angle is 82degrees for higher linearity.

13. A fluid amplifier as defined in claim 10, wherein the axialdistances between the first means and the portion of the control nozzlefurther therefrom is in the range of 0.047 inch to 0.057 inch.

14. A fluid amplifier as defined in claim 13, wherein said distance is0.047 inch for a high pressure gain characteristic.

15. A fluid amplifier as defined in claim 4, wherein the axis of saidoutlet passage means intersects the axis of said first means.

16. A fluid amplifier as defined in claim 7, and further including meansdefining a low pressure region between said first means and saidreceiver portion whereby modification of one of said streams causesproportional distribution of said resulting stream between saidreceiving means and said low pressure region.

17. A fluid amplifier as defined in claim 7, wherein the intersection ofsaid first and outlet passage means defines a splitter and an orifice insaid receiver portion, the axis of said first means being substantiallyaligned with said splitter.

18. A fluid amplifier as defined in claim 7, wherein the intersection ofsaid first and second passage means defines a splitter in said receiverportion between said passages, said receiver portion having a tip in thepath of said first stream through which the first and second passagesopen defining an orifice, the edge of the orifice and the axial locationof the splitter being defined by the equation,

2W Q Z-cos2 2d tan 21. A fiuid amplifier as defined in claim 7, whereinsaid first and second passage means have an included angle ofapproximately thirty degrees.

22. A fluid amplifier as defined in claim 21, wherein said includedangle is substantially bisected by the axis of said first means.

23. A fluid amplifier as defined in claim 7, wherein said receiverportion has a tip in the path of flow of said first stream, saidpassages opening at said tip, said first means having an exit portionspaced from said tip approximately 0.180 inch for high pressure recoverywhen the supply flow from said first means is under a high pressure.

24. A fluid amplifier as defined in claim 5, wherein said first meansincludes a primary supply nozzle, said nozzle having a convergentconical upstream portion and a cylindrical downstream exit portion, saidconical portion defining an angle of approximately fifteen degrees withthe axis of said passage, said passage having a length at least tentimes the diameter thereof.

References Cited UNITED STATES PATENTS 3,170,476 2/1965 Reilly 13781.53,187,763 6/1965 Adams 13781.5 3,238,959 3/19'66 Bowles 13781.S3,233,622 2/1966 vBoothe 137-81.5 3,272,215 9/1966 Bjornsen et a1137-81.5 3,295,543 1/1967 Zalmanzon 13781.5 3,323,532 6/1967 Campagnuolo13781.5 3,331,379 7/1967 Bowles 13781.5 3,362,421 1/1968 Schaifer137Sl.5

SAMUEL SCOTT, Primary Examiner

